Theory for In-Situ Thermal Diffusivity Measurement of Thin Films by a Radial Heat Flow Method

Abstract

Because of physical limitations of some materials which are used for thin films (such as thickness, stress tolerance and strength) it is sometimes advantageous to measure their thermal diffusivity after they have been deposited on a substrate, i.e. in—situ. Larson and Koyama** have proposed a method for in—situ thermal diffusivity measurement of thin films. Their method is an extension of the standard pulse method to a two—layer composite, i.e. one dimensional conduction following an instantaneous energy source on the surface of the film. In the data. analysis for their method, the temperature excursion at the rear surface of the substrate is utilized. This method lacks sensitivity to the thermal properties of the film, particularly if the substrate is thick or of low thermal diffusivity. Alternatively, we propose a method whereby a pulse of energy is deposited uniformly over a central circular region of film surface. In the process of thermal equilibration, locations on the surface of the film outside the initially heated region will undergo a temperature excursion. Through a theoretical analysis of the problem, the characteristics of this excursion and other (presumably known) factors can be utilized in the determination of the thermal diffuivity of the film.

This work was supported by the U.S. Energy Research and Development Administration.